APPENDIX 293 2. i>y distillation with potassium cyanide, the nitriles are obtained, (V.N-.SO.jK | KCN = (yir.CN -I- K,,SOa. ii •> <» i) i) j «j§ 3. 11 y fusion with sodium formate, the sulphonic group is replaced by carboxyl, r,;Il:iS():,Na ! IICOONa ---C,lI5COONaH- NallSOg. 4 l>y the action of phosphorus pentachloride the sulphonic chloride is obtained, rt;U,S()3K -I VL\ = (yiflSOXl + POC13 + KC1. PRKI'ARATION 75. Benzenesnlphonic Chloride.— The sulphonic chlorides differ from the carboxylic chlorides in being" very slowly decom- posed by water. They read, however, in an analogous fashion with alcohols, phenols, and amines in presence of caustic soda. The behaviour of primary, secondary, and tertiary amines has been sut^ested as a basis of separation of these three classes of compounds. The primary amines usually form compounds with tin1 sulphonic chloride, which dissolve in caustic soda ; the derivatives of the secondary amine are insoluble, whereas the tertiary amines do not re;ict with the sulphonic chloride (Hins- bcr^). The* method cannot always be employed. On reduction of the sulphonic chloride with zinc dust and water, the xinc salt of the sulphinic acid is formed, 2('(jIIfiS(),,ri -I- 2/n •= (Q.II-iSO.J.jXn + XnCl2. The arid is separatee! from the xinc salt by boiling with sodium carbonate, filtering from xinc carbonate, and decom- posing the soluble sodium salt with sulphuric acid, which pre- cipitates the sulphinic acid. The sulphinic acids are unstable compounds. They are readily oxidised to sulphonic acids ; on fusion with alkalis they are con- verted into the hydrocarbon and alkaline sulphite, CI!.S().N:i + NaOII = on reduction they form thiophenols, * Ct;ll,rS(UI -i 2llo -- QIUSIl -I 2lloO.